Divided wall distillation column for producing high purity normal butanol, and normal butanol distillation method

ABSTRACT

The present invention relates to a dividing wall distillation column for producing high-purity n-butanol, and a method for the production of high-purity n-butanol by fractional distillation. More particularly, the present invention relates to a method which provides a dividing wall distillation column with crude n-butanol as a feed to perform a fractional distillation of n-butanol, and an apparatus thereof. The dividing wall distillation column of the present invention exhibits the effects of a two distillation column from only one distillation column, thereby reducing energy and the costs of installing the apparatus as compared to conventional distillation systems.

This application is a continuation of application Ser. No. 13/145,325,filed Jul. 19, 2011, which is a National Stage Entry of InternationalApplication No. PCT/KR2010/000313 filed on Jan. 18, 2010 and claims thebenefit of priority to Korean Patent Application No. 10-2009-0004605filed on Jan. 20, 2009 and Korean Patent Application No. 10-2010-0003392filed on Jan. 14, 2010, the entire disclosures of which are incorporatedby reference in their entirety herein.

TECHNICAL FIELD

The present invention relates to a dividing wall distillation column forproducing high-purity n-butanol, and a method for the production ofhigh-purity n-butanol by fractional distillation.

BACKGROUND ART

Most raw materials such as crude oil are typically mixtures composed ofa number of compounds. Such raw materials are rarely used withoutpurification in industrial fields, and in most cases, they are separatedinto individual compounds before use. Distillation is a representativechemical process for separating mixtures into their respectivecomponents.

Generally, distillation serves to separate higher boiling components andlower boiling components from each other. (n−1) Distillation columns arerequired for the separation of a feed mixture composed of n components,where the number of columns is one larger than that of the components ofthe mixture. That is, in many cases, a conventional distillation processfor the separation of a three-component mixture into its individualcomponents employs a continuous two-column distillation system.

FIG. 1 illustrates a conventional two-column distillation system forseparating a three-component mixture into the individual components.

Referring to FIG. 1, the distillation system comprises a first column11, where a component D having the lowest boiling point is separatedfrom a component S having the intermediate boiling point and a componentB having the highest boiling point, and a second column 21, where thecomponents S and B are separated from each other.

The composition profile in the first column is shown in FIG. 2. As shownin FIG. 2, remixing of the intermediate boiling component (S) usuallyoccurs in the lower portion of the first column.

The conventional distillation process is advantageous in controlling thecompositions of the products, but remixing of the intermediate boilingcomponent in the first column takes place. This remixing results in lowthermodynamic efficiency of the distillation column system, bringingabout unnecessary additional energy consumption.

In order to solve such problems, a great deal of research has beenconducted on novel distillation systems. As a representative example, aPetlyuk distillation column for improving the separation efficiency of afeed mixture, which consists of a low boiling component, an intermediateboiling component and a high boiling component, by a thermally coupledstructure, is illustrated in FIG. 4. The Petlyuk distillation columncomprises a preliminary separator 12 and a main separator 22, which arearranged in a thermally coupled structure. The low boiling component andthe high boiling component are primarily separated from each other inthe preliminary separator, and then the top and bottom products areintroduced into respective feed plates of the main separator, where thelow boiling component, the intermediate boiling component and the highboiling component are separated from each other. This structureincreases the energy efficiency of the Petlyuk distillation columnbecause the distillation curves in the Petlyuk distillation columnbecome similar to the equilibrium distillation curve. However, thecolumn is not easy to design and operate. Particularly, it is difficultto balance the internal pressures of the columns.

To overcome the limitations of Petlyuk distillation columns, dividingwall distillation columns (DWCs) have been proposed. A dividing walldistillation column is similar to a Petlyuk distillation column from athermodynamic viewpoint, but they are structurally different from eachother. A typical dividing wall distillation column has a structure inwhich a dividing wall is installed to integrate a preliminary separatorand a main separator of a Petlyuk distillation column with each other.This structure solves the difficulties of the Petlyuk distillationcolumn, i.e. a difficulty in balancing the pressures of the preliminaryseparator and the main separator of the Petlyuk distillation column anda difficulty in operating the Petlyuk distillation column. In addition,the integration of the two separators greatly lowers the investment costof the Petlyuk distillation column.

Some distillation techniques for the production of n-butanol can befound in Korean Patent Publication No. 10-2003-0088211 A2 published onNov. 19, 2003 (‘Patent Publication 1’) and Korean Patent Publication No.10-2008-0099034 A1 published on Nov. 12, 2008 (‘Patent Publication 2’).

Patent Publication 1 suggests a method for purifying n-butanol usingonly two distillation columns. Specifically, the method comprises addingan alkaline additive to slop butanol as a raw material, which is a sideproduct created during the production of oxoalcohol, removing water andlow boiling materials from the mixture in a first distillation column 1,and removing high boiling materials from the remaining mixture in asecond distillation column 2. According to the method, since thetwo-column distillation system produces n-butanol in an amountcomparable to that of n-butanol produced by the operation of aconventional three-column distillation system, the number of processingsteps is reduced and the energy and cost required to operate thetwo-column distillation system are greatly reduced in comparison tothose of the conventional three-column distillation system.

Patent Publication 2 proposes a method comprising introducing a mixtureconsisting of a low boiling material A, an intermediate boiling materialB and a high boiling material C into a first distillation column;separating the mixture in the first distillation column to provide a topproduct and a bottom product of the first distillation column to preventremixing of the intermediate boiling material in the lower portion ofthe first distillation column; and separating the bottom product in thesecond distillation column to provide a top product and a bottom productof the second distillation column, thereby controlling the concentrationratio between the intermediate boiling material B and the low boilingmaterial A in the top product of the second distillation column.

DISCLOSURE Technical Problem

Dividing wall distillation columns of the prior art are not practicallyused in industrial fields despite their advantages. The main reason forthis is that once designed, the structural disability of dividing walldistillation columns to control the internal circulating rate leads tolack of flexibility depending on variations of operational conditions,unlike Petlyuk distillation columns. That is, accurate simulation andstructure determination of dividing wall distillation columns arerequired at the initial stage of design.

A great deal of research is currently being conducted on the structureand control of dividing wall distillation columns. However, the designstructures and operational conditions of dividing wall distillationcolumns are very limited. Examples of the design structures of adividing wall distillation column include the position of a feed plate,the installation zone of a dividing wall, the position of a plate wherean intermediate boiling material is produced, and the total number ofplates. Examples of the operational conditions of a dividing walldistillation column include distillation temperature and pressureconditions.

Particularly, the design structures (e.g., the number of plates and theposition of a feed plate) and the operational conditions (e.g.,distillation temperature and pressure conditions) of a dividing walldistillation column should be specially varied depending on thecharacteristics of a compound to be separated by fractional distillationin the dividing wall distillation column. Such limitations make itdifficult to use dividing wall distillation columns.

The present invention has been made in view of the problems of the priorart. The objective of the present invention is to provide a dividingwall distillation column suitably designed to purify n-butanol withreduced energy at low installation costs. Another objective of thepresent invention is to provide a method for operating the dividing walldistillation column.

Technical Solution

According to an aspect of the present invention, there is provided adividing wall distillation column comprising a condenser; a reboiler;and a main column including a dividing wall installed therein, whereinthe main column is divided into a top zone, an upper feed zone, an upperoutflow zone, a lower feed zone, a lower outflow zone and a bottom zone,and wherein the main column has at least one inflow and at least threeoutflows, the inflow being a stream of crude n-butanol as a feed Fflowing into an intermediate feed plate NR1, where the upper feed zoneand the lower feed zone of the main column are in contact with eachother, and at least one of the outflows is substantially a stream ofn-butanol.

According to another aspect of the present invention, there is provideda dividing wall distillation column comprising a condenser; a reboiler;and a main column including a dividing wall installed therein, whereinthe main column is divided into a top zone, an upper feed zone, an upperoutflow zone, a lower feed zone, a lower outflow zone and a bottom zone,and wherein crude n-butanol as a feed F flows into an intermediate feedplate NR1, where the upper feed zone and the lower feed zone of the maincolumn are in contact with each other, a low boiling component D flowsout of the top zone, a high boiling component B flows out of the bottomzone and an intermediate boiling component S flows out of anintermediate outflow plate NR2, where the upper outflow zone and thelower outflow zone are in contact with each other, and the intermediateboiling component S is substantially n-butanol.

In an embodiment, the feed F contains at least 90% by weight ofn-butanol.

In an embodiment, the number of plates in each of the top zone, theupper feed zone, the upper outflow zone, the lower feed zone, the loweroutflow zone and the bottom zone of the main column is in the range of80 to 145% of the number of theoretical plates in the correspondingzone, as calculated by distillation curves.

In an embodiment, the length of the dividing wall is determineddepending on the number of plates in the upper feed zone and the lowerfeed zone or the number of plates in the upper outflow zone and thelower outflow zone.

In an embodiment, the dividing wall has a length in the range of 30 to85% of the total number of theoretical plates in the top zone, the upperfeed zone, the lower outflow zone and the bottom zone, as calculated bydistillation curves.

In an embodiment, the temperature of the top zone is in the range of 90to 100° C. at ambient pressure.

In an embodiment, the temperature of the bottom zone is in the range of140 to 160° C. at ambient pressure.

In an embodiment, the temperature of the intermediate outflow plate NR2,which is provided in a position where the upper outflow zone and thelower outflow zone are in contact with each other and from which theintermediate boiling component S flows, is in the range of 118 to 127°C. at ambient pressure.

In an embodiment, the temperature of the top zone is in the range of alower limit temperature T_(1a) to an upper limit temperature T_(2a), ascalculated by the following equations 1:T _(1a)=86.8036×P ^(0.3570)T _(2a)=96.8276×P ^(0.3201)  (1)

wherein T_(1a) and T_(2a) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

In an embodiment, the temperature of the bottom zone is in the range ofa lower limit temperature T_(1b) to an upper limit temperature T_(2b),as calculated by the following equations 2:T _(1b)=139.100×P ^(0.1438)T _(2b)=156.9071×P ^(0.1977)  (2)

wherein T_(1b) and T_(2b) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

In an embodiment, the temperature of the intermediate outflow plate NR2,which is provided in a position where the upper outflow zone and thelower outflow zone are in contact with each other and from which theintermediate boiling component S flows, is in the range of a lower limittemperature T_(1c) to an upper limit temperature T_(2c), as calculatedby the following equations 3:T _(1c)=115.7594×P ^(0.2297)T _(2c)=125.0420×P ^(0.2727)  (3)

wherein T_(1c) and T_(2c) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

According to yet another aspect of the present invention, there isprovided a method for producing n-butanol from crude n-butanol as a feedF by fractional distillation in a dividing wall distillation column,wherein the dividing wall distillation column comprises a condenser; areboiler; and a main column including a dividing wall installed therein,the main column being divided into a top zone, an upper feed zone, anupper outflow zone, a lower feed zone, a lower outflow zone and a bottomzone, and wherein a low boiling component D flows out of the top zone, ahigh boiling component B flows out of the bottom zone and anintermediate boiling component S flows out of an intermediate outflowplate NR2, where the upper outflow zone and the lower outflow zone arein contact with each other, and the intermediate boiling component S issubstantially n-butanol.

In an embodiment, the feed F contains at least 90% by weight ofn-butanol.

In an embodiment, the number of plates in each of the top zone, theupper feed zone, the upper outflow zone, the lower feed zone, the loweroutflow zone and the bottom zone of the main column is in the range of80 to 145% of the number of theoretical plates in the correspondingzone, as calculated by distillation curves.

In an embodiment, the length of the dividing wall is determineddepending on the number of plates in the upper feed zone and the lowerfeed zone or the number of plates in the upper outflow zone and thelower outflow zone.

In an embodiment, the dividing wall has a length in the range of 30 to85% of the total number of theoretical plates in the top zone, the upperfeed zone, the lower outflow zone and the bottom zone, as calculated bydistillation curves.

In an embodiment, the temperature of the top zone is in the range of 90to 100° C. at ambient pressure.

In an embodiment, the temperature of the bottom zone is in the range of140 to 160° C. at ambient pressure.

In an embodiment, the temperature of the intermediate outflow plate NR2,which is provided in a position where the upper outflow zone and thelower outflow zone are in contact with each other and from which theintermediate boiling component S flows, is in the range of 118 to 127°C. at ambient pressure.

In an embodiment, the temperature of the top zone is in the range of alower limit temperature T_(1a) to an upper limit temperature T_(2a), ascalculated by the following equations 1:T _(1a)=86.8036×P ^(0.3570)T _(2a)=96.8276×P ^(0.3201)  (1)

wherein T_(1a) and T_(2a) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

In an embodiment, the temperature of the bottom zone is in the range ofa lower limit temperature T_(1b) to an upper limit temperature T_(2b),as calculated by the following equations 2:T _(1b)=139.100×P ^(0.1438)T _(2b)=156.9071×P ^(0.1977)  (2)

wherein T_(1b) and T_(2b) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

In an embodiment, the temperature of the intermediate outflow plate NR2,which is provided in a position where the upper outflow zone and thelower outflow zone are in contact with each other and from which theintermediate boiling component S flows, is in the range of a lower limittemperature T₁, to an upper limit temperature T_(2c), as calculated bythe following equations 3:T _(1c)=115.7594×P ^(0.2297)T _(2c)=125.0420×P ^(0.2727)  (3)

wherein T_(1c) and T_(2c) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

Advantageous Effects

The dividing wall distillation column of the present invention has thesame effects as two-column distillation systems from only onedistillation column. Therefore, the dividing wall distillation column ofthe present invention possesses the advantages of reduced energyconsumption and low installation costs, compared to conventionaldistillation systems.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a conventional distillationsystem for separating a three-component mixture;

FIG. 2 shows the composition profile in a first column of thedistillation system of FIG. 1;

FIG. 3 shows the composition profile in a conventional one-columndistillation system that is operated with a lateral outflow;

FIG. 4 is a schematic view illustrating the structure of a Petlyukdistillation column;

FIG. 5 is a schematic view illustrating the structure of a dividing walldistillation column according to an embodiment of the present invention;

FIG. 6 is a schematic view illustrating a comparative distillationcolumn system; and

FIG. 7 is a schematic view illustrating an inventive dividing walldistillation column.

EXPLANATION OF ESSENTIAL PARTS OF THE DRAWINGS

1: Main column 11: First column 21: Second column 12: Preliminaryseparator 22: Main separator 31: Condenser 41: Reboiler 51: Dividingwall 100: Top zone 200: Upper feed zone 300: Upper outflow zone 400:Lower feed zone 500: Lower outflow zone 600: Bottom zone NR1:Intermediate feed plate NR2: Intermediate outflow plate F: Feed B: Highboiling material D: Low boiling material S: Intermediate boilingmaterial

BEST MODE

Hereinafter, the present invention will be explained in more detail withreference to the following examples. However, these examples areprovided for illustrative purposes only and are not intended to limitthe scope of the present invention.

EXAMPLES

An inventive dividing wall distillation column (DWC) using a singlecolumn was designed, constructed and operated as proposed in the presentinvention to verify its performance. As a result, it was confirmed thata desired composition of the final product was obtained. A comparativetwo-column distillation system having no dividing wall was constructed.

FIGS. 6 and 7 illustrate the comparative distillation system and theinventive dividing wall distillation column, respectively. Referencenumerals 1 to 8 in FIG. 6 indicate individual streams of the comparativedistillation system, and reference numerals 1 to 6 in FIG. 7 indicateindividual streams in the inventive dividing wall distillation column.

The numbers of theoretical plates in the zones of the inventive dividingwall distillation column and the zones of the comparative distillationsystem are shown in Table 2. The experimental results are shown inTables 3 and 4. The top zone of the inventive dividing wall distillationcolumn had a temperature of about 95° C. The streams 2, 3 and 4 havingpassed through a condenser in the inventive dividing wall distillationcolumn were cooled to about 50° C.

TABLE 2 Zone Number of theoretical plates Inventive Top zone 100 10dividing Upper feed zone 200 5 wall Upper outflow zone 300 10distillation Lower feed zone 400 25 column Lower outflow zone 500 20Bottom zone 600 15 Comparative First column 20 distillation Secondcolumn 32 system

TABLE 3 Unit 1 2 3 4 5 6 7 8 Comparative Conditions Temp. ° C. 87 97 9797 129.7 50 50 150.2 distillation Pressure Kgf/cm² 5 1.09 1.09 1.094.033 1.79 1.79 1.874 system Flow kg/hr 15823 3430 86.5 65.5 1567123268.2 15208 463 rate Composition H₂O wt % 0.6 8.7 100 8.7 0 0 0 0Light 0.11 2.6 0 2.6 0.1 0.1 0.1 0 n- 97.3 88.7 0 88.7 97.9 99.9 99.930.9 BuOH Heavies 2 0 0 0 2 0 0 69 Inventive Conditions Temp. ° C. 87 5050 50 122.6 149.7 — — dividing wall Pressure kgf/cm² 5 1.09 1.09 1.091.235 1.54 — — distillation Flow kg/hr 15823 13910 82.5 131.5 15208 401— — column rate Composition H₂O wt % 0.6 41.7 79.4 18.1 0 0 — — Light0.11 3 0.8 4.25 0.05 0 — — n- 97.3 55.3 19.8 77.6 99.9 20.8 — — BuOHHeavies 2 0 0 0 0.02 79.12 — —

TABLE 4 Comparative distillation system Inventive dividing First Secondwall distillation Reduced amount Reduction Total column column column(MMKcal/hr) rate (%) Amount of energy 7.90 1.21 6.69 5.50 2.40 30.4consumed (MMKcal/hr)

As can be seen from the above results, remixing was prevented in theinventive dividing wall distillation column and the separationefficiency of the inventive dividing wall distillation column increased,resulting in efficient production of n-butanol having a purity of 99.9wt %. Due to the increased purity of the product, the number ofadditional rectification recycle steps of n-butanol was reduced and theproductivity of n-butanol was improved. The inventive dividing walldistillation column, which comprises a single column and two heatexchangers, was advantageous in terms of investment cost when comparedto the comparative distillation column system, which comprises twocolumns and four heat exchangers. In addition, the inventive dividingwall distillation column showed a 30.4% reduction rate in energyconsumption compared to the comparative distillation column system.

MODE FOR INVENTION

The present invention will now be described in detail.

FIG. 5 illustrates the structure of a dividing wall distillation columnaccording to an embodiment of the present invention. The invention willbe better understood with reference to FIG. 5 and the followingexplanation.

The dividing wall distillation column comprises a condenser; a reboiler;and a main column including a dividing wall installed therein, whereinthe main column is divided into a top zone, an upper feed zone, an upperoutflow zone, a lower feed zone, a lower outflow zone and a bottom zone,and wherein the main column has at least one inflow and at least threeoutflows, the inflow being a stream of crude n-butanol as a feed Fflowing into an intermediate feed plate NR1, where the upper feed zoneand the lower feed zone of the main column are in contact with eachother, and at least one of the outflows is substantially a stream ofn-butanol.

In an alternative embodiment, there is provided a dividing walldistillation column comprising a condenser; a reboiler; and a maincolumn including a dividing wall installed therein, wherein the maincolumn is divided into a top zone, an upper feed zone, an upper outflowzone, a lower feed zone, a lower outflow zone and a bottom zone, andwherein crude n-butanol as a feed F flows into an intermediate feedplate NR1 where the upper feed zone and the lower feed zone of the maincolumn are in contact with each other, a low boiling component D flowsout of the top zone, a high boiling component B flows out of the bottomzone and an intermediate boiling component S flows out of anintermediate outflow plate NR2, where the upper outflow zone and thelower outflow zone are in contact with each other, and the intermediateboiling component S is substantially n-butanol.

The dividing wall distillation column of the present invention comprisesa condenser 31 and a reboiler 41.

The condenser 31 is a unit that absorbs heat of vaporization from agaseous mixture to condense the gaseous mixture. The condenser 31 may beany suitable condenser used among conventional chemical engineeringequipment.

The reboiler 41 is a unit that provides heat of vaporization to a liquidmixture to vaporize the liquid mixture. The reboiler 41 may be anysuitable reboiler used among conventional chemical engineeringequipment.

The main column 1 can be largely divided into six zones.

The top zone 100 indicates an upper region of the main column that isnot partitioned by the dividing wall.

The upper feed zone 200 is a sub-region that is partitioned by thedividing wall at one side thereof and is positioned over the stream ofthe inflowing material (i.e. the feed).

The upper outflow zone 300 is a sub-region that is partitioned by thedividing wall at one side thereof and is positioned over the stream ofthe outflowing material.

The lower feed zone 400 is a sub-region that is partitioned by thedividing wall at one side thereof and is positioned under the stream ofthe inflowing material.

The lower outflow zone 500 is a sub-region that is partitioned by thedividing wall at one side thereof and is positioned under the stream ofthe outflowing material.

The bottom zone 600 indicates a lower region of the main column that isnot partitioned by the dividing wall.

The main column has at least one inflow and at least three outflows.

The feed F (i.e. crude n-butanol) flows into the intermediate feed plateNR1, where the upper feed zone and the lower feed zone of the maincolumn are in contact with each other, the low boiling component D flowsout of the top zone, a high boiling component B flows out of the bottomzone, and the intermediate boiling component S flows out of theintermediate outflow plate NR2, where the upper outflow zone and thelower outflow zone are in contact with each other. The intermediateboiling component S flowing out of the intermediate outflow plate NR2 issubstantially n-butanol.

The term “crude n-butanol” as used herein refers to a mixture containingn-butanol as a main component and is a material to be distilled in thedividing wall distillation column. The term “main component” means acomponent that composes the larger portion of the mixture than the othercomponents of the mixture. A higher content of n-butanol in the cruden-butanol is preferred for higher purity. It is preferred to use cruden-butanol having an n-butanol content of at least 90 wt % in order toobtain n-butanol having purity as high as 99 wt %.

The phrase “substantially n-butanol” means that the mixture per se canbe substantially considered as n-butanol. Specifically, the phrase meansthat n-butanol as a main component is present in an amount larger thanthe n-butanol content of the feed and exceeding at least 90 wt % withrespect to the total weight of the mixture.

The structural difference between dividing wall distillation andcontinuous two-column distillation accounts for the reason why dividingwall distillation consumes less energy than the continuous two-columndistillation. In the dividing wall distillation column, the spacesdivided by the dividing wall serve as preliminary separators to separatethe high boiling material and the low boiling material. This separationrenders the liquid composition coinciding with the equilibriumdistillation curve and inhibits the occurrence of remixing, leading toimproved thermodynamic efficiency for separation.

The upper feed zone and the lower feed zone of the dividing walldistillation column act like preliminary separators of the conventionaldistillation column. The upper and lower feed zones of the dividing walldistillation column can be collectively referred to as a preliminaryseparation region. Three components flowing into the preliminaryseparation region are separated into a low boiling material and a highboiling material. The low boiling material and a portion of the highboiling material flow into the top zone, and portions thereof flow intothe upper outflow zone and the lower outflow zone, where they arere-distilled.

The upper and lower outflow zones act like main separators of theconventional distillation column. The upper and lower outflow zones ofthe dividing wall distillation column can be collectively referred to asa main separation region. The low boiling material and the intermediateboiling material are predominantly separated in the upper portion of themain separation region. The intermediate boiling material and the highboiling material are predominantly separated in the lower portion of themain separation region.

After the low boiling component passes through the top zone of the maincolumn and the condenser, a portion of the low boiling component isproduced as a low boiling product D and the other portion thereofreturns in the form of a liquid stream LD to the top zone of the maincolumn. After the high boiling component passes through the bottom zoneof the main column and the reboiler, a portion of the high boilingcomponent is produced as a high boiling product B and the other portionthereof returns in the form of a vapor stream VB to the bottom zone ofthe main column.

The design of the thermally coupled distillation column system havingthe dividing wall therein is based on the design of the conventionalthermally coupled distillation column having a minimum number of plates.The efficiency of the distillation column reaches a maximum value whenthe liquid composition distribution in the distillation plate of thecolumn is close to the equilibrium distillation curve. Based on this,the distillation system of the present invention is designed to have aminimum number of plates on the assumption that the distillation columnis operated by total reflux distillation. That is, the upper feed zoneand the lower feed zone are designed under an assumption that the liquidcomposition is the same as the feed composition in the liquid in thefeed plate, and the upper outflow zone and the lower outflow zone aredesigned by calculating the liquid compositions in the column from themiddle portion to the top of the column, starting from the concentrationof the intermediate boiling product, by a stepwise equilibration designmethod, and the lower outflow zone acting as a main separator isdesigned by stepwise calculating the liquid compositions in the columnfrom the middle portion to the bottom of the column, starting from theconcentration of the intermediate boiling product, by an equilibrationdesign method. From the obtained liquid composition distribution, thefeed plate and the numbers of plates having the compositions of therespective products can be counted to determine the numbers of plates inthe upper and lower feed zones acting as preliminary separators and thenumber of plates in the upper and lower outflow zones acting as mainseparators. The number of plates in the respective zones is atheoretical and ideal value. In an actual case, it is preferred toadjust the number of plates in the column to 80 to 145% of the number oftheoretical plates in accordance with common design criteria. If thenumber of plates in the column is less than 80% of the calculated numberof theoretical plates, the low boiling material and the high boilingmaterial may not be sufficiently separated from each other in thepreliminary separation region. Meanwhile, if the number of plates in thecolumn exceeds 145% of the calculated number of theoretical plates,which corresponds to the minimum reflux ratio, the investment costsundesirably increases without a further reduction in energy consumption.

The length of the dividing wall installed in the main column isdetermined depending on the number of plates calculated from thedistillation curves of the upper feed zone and the lower feed zone orthe upper outflow zone and the lower outflow zone.

The number of theoretical plates and the refluxed amount in the dividingwall distillation column can be calculated by various methods, forexample, by plotting equilibrium distillation curves with respect to theliquid compositions in the preliminary separation region and the mainseparation region to design an optimum zone for the dividing wall in thedividing wall distillation column. The number of theoretical plates inthe dividing wall distillation column of the present invention isdetermined by the Fenske-Underwood equation, which is well known tothose ordinarily skilled in the art.

It is preferred that the length of the dividing wall be within the rangeof 30 to 85% of the total number of theoretical plates in the top zone,the upper feed zone, the lower outflow zone and the bottom zone, ascalculated by distillation curves. If the length of the dividing wall isless than 30% of the number of theoretical plates, a portion of the lowboiling material may fall down from the preliminary separation regionand may be included in the product of the main separator. Meanwhile, ifthe length of the dividing wall is more than 85% of the number oftheoretical plates, it is difficult to maintain smooth equilibrium flowsof the liquid/vapor of the low/intermediate boiling materials and theliquid/vapor of the intermediate/high boiling materials, which may causeproblems in the construction of the column.

The temperature of the top zone of the main column is preferably in therange of 90 to 100° C. at ambient pressure. If the top zone has atemperature lower than 90° C., the low boiling material may fall downfrom the preliminary separation region to adversely affect the purity ofthe product. Meanwhile, if the top zone has a temperature higher than100° C., the high boiling material (heavies) may ascend the preliminaryseparation region to adversely affect the purity of the product.

The temperature of the bottom zone of the main column is preferably inthe range of 140 to 160° C. at ambient pressure. If the bottom zone hasa temperature lower than 140° C., the intermediate boiling material(n-butanol) falls down, resulting in a low yield of the product.Meanwhile, if the bottom zone has a temperature higher than 160° C.,there is the danger that the high boiling material (i.e. heavies) mayflow laterally out of the column, together with the intermediate boilingmaterial (n-butanol).

The temperature of the intermediate outflow plate NR2, which is providedin a position where the upper outflow zone and the lower outflow zoneare in contact with each other, and from which the intermediate boilingcomponent S flows, is in the range of 118 to 127° C. at ambientpressure. If the intermediate outflow plate has a temperature lower than118° C., it is not easy to remove the low boiling material from theintermediate outflow plate. Meanwhile, if the intermediate outflow platehas a temperature higher than 127° C., it is not easy to remove the highboiling material from the intermediate outflow plate. That is, thetemperature of the intermediate outflow plate NR2 may have a greatinfluence on the purity of the product.

The temperature ranges of the top zone, the bottom zone, and theintermediate outflow plate NR2 of the main column are values measured atambient pressure. The ambient pressure as used herein is around 1.09kgf/cm² and has a slightly different meaning from the atmosphericpressure (i.e. 1 atm≈1.033 kgf/cm²), which is commonly understood asambient pressure. Considering the fact that distillation columns areusually operated at pressures slightly higher than the atmosphericpressure, a pressure of about 1.09 kgf/cm² is commonly recognized asambient pressure in chemical factories where many high-pressureprocesses are performed.

In the case where the dividing wall distillation column is operated at apressure higher or lower than ambient pressure, it is necessary tocontrol the upper limit and lower limit temperatures of the respectivezones depending on the pressure. That is, the temperature ranges of thezones may be varied when the dividing wall distillation column isoperated under increased or reduced pressure. Generally, the upper andlower limit temperatures tend to increase as the operating pressureincreases.

For example, when the dividing wall distillation column is operated at apressure of about 0.8 kgf/cm², it is preferred to adjust the temperatureranges of the top zone, the bottom zone and the intermediate outflowplate NR2 to about 80 to 90° C., about 135 to 150° C. and about 110 to118° C., respectively.

When the dividing wall distillation column is operated at a pressure ofabout 1.3 kgf/cm², it is preferred to adjust the temperature ranges ofthe top zone, the bottom zone and the intermediate outflow plate NR2 toabout 95 to 105° C., about 145 to 165° C. and about 123 to 135° C.,respectively.

Table 1 summarizes the upper and lower limit temperatures of the topzone, the bottom zone and the intermediate outflow plate NR2 atdifferent operating pressures of the dividing wall distillation column.

TABLE 1 Lower limit Upper limit Temp. (° C.) Temp. (° C.) P ≈ 1.09kgf/cm² (at ambient pressure) Top zone 90 100 Bottom zone 140 160Intermediate outflow plate NR2 118 127 P ≈ 0.8 kgf/cm² (at reducedpressure) Top zone 80 90 Bottom zone 135 150 Intermediate outflow plateNR2 110 118 P ≈ 1.3 kgf/cm² (at raised pressure) Top zone 95 105 Bottomzone 145 165 Intermediate outflow plate NR2 123 135

Particularly, when the top zone is not at ambient pressure, thetemperature of the top zone may be in the range of a lower limittemperature T_(1a) to an upper limit temperature T_(2a), as calculatedby the following equations 1:T _(1a)=86.8036×P ^(0.3570)T _(2a)=96.8276×P ^(0.3201)  (1)

wherein T_(1a) and T_(2a) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

When the bottom zone is not at ambient pressure, the temperature of thebottom zone may be in the range of a lower limit temperature T_(1b) toan upper limit temperature T_(2b), as calculated by the followingequations 2:T _(1b)=139.100×P ^(0.1438)T _(2b)=156.9071×P ^(0.1977)  (2)

wherein T_(1b) and T_(2b) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

When the intermediate outflow zone NR2 is not at ambient pressure, thetemperature of the intermediate outflow zone may be in the range of alower limit temperature T_(1c) to an upper limit temperature T_(2c), ascalculated by the following equations 3:T _(1c)=115.7594×P ^(0.2297)T _(2c)=125.0420×P ^(0.2727)  (3)

wherein T_(1c) and T_(2c) represent a temperature expressed in degreesCelsius (° C.), and P represents a pressure expressed in kgf/cm² and isfrom 0.1 to 10, with the proviso that P is not 1.09.

The above equations are derived by using the least square method basedon the data in Table 1.

The thermally coupled distillation column system of the presentinvention aims to improve the distillation efficiency of athree-component mixture. This distillation system is constructed suchthat the dividing wall is installed in the main column to form spacesacting as a preliminary separator and a main separator, each of whichhas a liquid composition distribution similar to a high-efficiencyequilibrium distillation system. Therefore, the distillation system ofthe present invention has the same effects as two-column distillationsystems.

The present invention also provides a method for producing n-butanolfrom crude n-butanol as a feed by fractional distillation in a dividingwall distillation column, wherein the dividing wall distillation columncomprises a condenser; a reboiler; and a main column including adividing wall installed therein, the main column being divided into atop zone, an upper feed zone, an upper outflow zone, a lower feed zone,a lower outflow zone and a bottom zone, and wherein a low boilingcomponent D flows out of the top zone, a high boiling component B flowsout of the bottom zone and an intermediate boiling component S flows outof an intermediate outflow plate NR2, where the upper outflow zone andthe lower outflow zone are in contact with each other, and theintermediate boiling component S is substantially n-butanol.

In an embodiment, the number of plates in each of the top zone, theupper feed zone, the upper outflow zone, the lower feed zone, the loweroutflow zone and the bottom zone is in the range of 80 to 150% of thenumber of theoretical plates in the corresponding zone, as calculated bydistillation curves.

In an embodiment, the length of the dividing wall is determineddepending on the number of plates in the upper feed zone and the lowerfeed zone or the number of plates in the upper outflow zone and thelower outflow zone.

In an embodiment, the dividing wall has a length in the range of 30 to85% of the total number of theoretical plates in the top zone, the upperfeed zone, the lower outflow zone and the bottom zone, as calculated bydistillation curves.

In an embodiment, the temperature of the top zone is in the range of 90to 100° C. at ambient pressure.

In an embodiment, the temperature of the bottom zone is in the range of140 to 160° C. at ambient pressure.

In an embodiment, the temperature of the intermediate outflow plate NR2,which is provided in a position where the upper outflow zone and thelower outflow zone are in contact with each other and from which theintermediate boiling component S flows, is in the range of 118 to 127°C. at ambient pressure.

In an embodiment, when the top zone is not at ambient pressure, thetemperature of the top zone is in the range of a lower limit temperatureT_(1a) to an upper limit temperature T_(2a), as calculated by Equations1.

In an embodiment, when the bottom zone is not at ambient pressure, thetemperature of the bottom zone is in the range of a lower limittemperature T_(1b) to an upper limit temperature T_(2b), as calculatedby Equations 2.

In an embodiment, when the intermediate outflow plate NR2, which isprovided in a position where the upper outflow zone and the loweroutflow zone are in contact with each other and from which theintermediate boiling component S flows, is not at ambient pressure, thetemperature of the intermediate outflow plate is in the range of a lowerlimit temperature T_(1c) to an upper limit temperature T_(2c), ascalculated by Equations 3.

The invention claimed is:
 1. A dividing wall distillation columncomprising a condenser; a reboiler; and a main column including adividing wall installed therein, wherein the main column is divided intoa top zone, an upper feed zone, an upper outflow zone, a lower feedzone, a lower outflow zone and a bottom zone, and wherein the maincolumn has at least one inflow and at least three outflows, the inflowbeing a stream of crude n-butanol as a feed flowing into an intermediatefeed plate, where the upper feed zone and the lower feed zone of themain column are in contact with each other, and at least one of theoutflows is substantially a stream of n-butanol, wherein a temperatureof the top zone is in the range of 90 to 100° C. at ambient pressure, atemperature of an intermediate outflow plate at a position where theupper outflow zone and the lower outflow zone are in contact with eachother is in the range of 118 to 127° C. at ambient pressure, and atemperature of the bottom zone is in the range of 140 to 160° C. atambient pressure, and wherein the inflow is a stream of a feedcontaining at least 90% by weight of n-butanol flowing into anintermediate feed plate.
 2. A method for producing a feed of n-butanolfrom crude n-butanol, wherein the method comprises fractionaldistillation of the crude n-butanol in a dividing wall distillationcolumn according to claim 1.